This invention relates to a locking device for use on drafting board tables in which a drafting board is adjustably inclined to a desired selected angle by the draftsman to facilitate his work thereon. Each draftsman usually has a preferred drafting board angle depending upon the draftsman's physical characteristics, the height of the drafting table and the location of the drawing on the board.
Prior proposed constructions for adjusting the tilt angle of a drawing board on a drafting table have included the provision of rack bars having rack teeth on the table and engaged by pivoted legs, interconnected transversely, carried by the drafting board. Multiple adjustment of the inclination of the table in increments was related to the spacing of the track teeth on the bar. When the pivoted legs were interconnected, then the entire leg structure was required to be manipulated to properly engage the legs with the rack teeth. In the event the legs were not interconnected, then the draftsman was required to adjust each leg at each side of the table.
Another proposed prior construction was to pivotally connect a rod to each side of the drafting table and provide a knob with a friction screw on the drafting table for slidable adjustment of each rod to a desired board position. To accomplish such adjustment, the draftsman was required to go each side of the table to adjust the friction screw by the knob. Intermediate adjustments were awkward to make because of the weight of the table and the necessity for precise individual adjustment at each side of the table.
Pneumatically operated door closures are often provided with a slidable washer on the piston rod of the door closure, the washer having an axial extending portion adapted to abut one end of a cylinder to position the wahser at an angle to frictionally prevent further sliding of the piston rod within the cylinder at a selected open position of the door. Such lock washer was provided with a circular hole through which the circular cross sectional piston rod passed. Frictional engagement of the edge margins of the hole with the rod occurred essentially at a tangent of the cylindrical surface of the rod with the circular edge margins of the hole in the washer. Loads in such a door closure are not substantial, and the lock washer was not secured to another member and such minimal frictional contact was acceptable.